1. Field of the Invention
The present invention relates to a vehicle body structure of a motorcycle which is provided with a vehicle body frame and a swing arm for a rear wheel, and a rear suspension interposed between both the vehicle body frame and the swing arm.
2. Description of the Related Art
In a motorcycle having a rear suspension for a rear wheel, in general, the rear suspension is arranged in a center of a vehicle width, and a front end portion of the rear suspension is coupled to a cross member of a vehicle body frame of the motorcycle. A load applied from a swing arm for supporting the rear wheel is transmitted to the vehicle body frame via the cross member.
As another arrangement example of the rear suspension, there is a motorcycle in which the rear suspension is arranged in a side of an engine arranged within the vehicle body frame, and the rear suspension is interposed between the front end portion of the vehicle body frame and the swing arm (refer, for example, to Japanese Unexamined Patent Publication No. 2001-106155).
As in the prior art, if the rear suspension is arranged near the center of the vehicle width, various parts arranged around the rear suspension form obstacles to performing maintenance of the rear suspension, therefore, it is difficult to perform a repair, cleaning or the like. Further, the rear suspension can not be utilized as a mechanical (functional) appearance element since the rear suspension is under an approximately hindered state from an external side of the vehicle body frame.
Further, if the front end portion of the rear suspension is coupled to the cross member of the vehicle body frame, the load applied from the swing arm is first transmitted to the cross member, and is then transmitted to a main frame member or the like of the vehicle body frame. However, since the cross member is a member arranged in a vehicle width direction, the cross member receives a bending load. Further, since the rear suspension is generally attached via a support bracket protruding from the cross member, the cross member receives a torsional moment. Accordingly, high rigidity is required in the cross member. As a result, an increase of weight of the cross member is caused, and an increase of weight of the vehicle body frame is caused by extension.
Therefore, there is a consideration to arrange the rear suspension so as to be displaced right or left from the center of the vehicle width. However, in this case, since a laterally biased load is applied to the swing arm coupling a rear end portion of the rear suspension, it is necessary to increase rigidity of the swing arm in comparison with the conventional one.
If the rigidity of the entirety of the swing arm is simply increased while keeping the aspect of the conventional swing arm as it is, the weight is widely increased. Further, since various parts such as a brake disc, a caliper, a drive chain and the like are arranged around the swing arm, it may be impossible to simply make pipes constituting the swing arm thick or large.
Further, in a structure in which the rear suspension is arranged in the side of the engine within the vehicle body frame such as the technique described in Japanese Unexamined Patent Publication No. 2001-106165 mentioned above, since the rear suspension protrudes from the side of the engine in a lateral direction, it is hard to obtain a compact structure, and there is a possibility that the rear suspension will form an obstacle to the legs of a rider and a fellow passenger. Further, since the rear suspension is arranged near the engine, oil or the like within the rear suspension is easily affected by a heat of the engine.